DOTLOCKFILE

NAME

dotlockfile - Utility to manage lockfiles

SYNOPSIS

/usr/bin/dotlockfile
[-p]
[-c]
[-m]
[-l|-u|-t]
[-rretries]
[lockfile]

DESCRIPTION

Dotlockfile is a command line utility to safely create, test and
remove lockfiles. Lockfiles are created in an NFS-safe way. Dotlockfile
can can also be used to lock and unlock mailboxes even if the mailspool
directory is only writable by group mail.

The name dotlockfile comes from the way mailboxes are locked for updates
on a lot of UNIX systems. A lockfile is created with the same filename
as the mailbox but with the string ".lock" appended.

The names dotlock and lockfile were already taken - hence
the name dotlockfile:).

OPTIONS

-l

Create a lockfile. This is the default.

-u

Remove a lockfile.

-c

Check for the existence of a valid lockfile.

-t

Touch an existing lockfile (update the timestamp).

-p

Write the process-id of the calling process into the lockfile. Also
when testing for an existing lockfile, check the contents for a process-id
to find out if the lockfile is still valid.

-r retries

The number of times dotlockfile retries to acquire the lock if it
failed the first time before giving up. The initial sleep after failing
to acquire the lock is 5 seconds. After each next try, a sleep of 5
seconds extra occurs up to a maximum sleep of 60 seconds between tries.
The default number of retries is 5.

-m

Lock or unlock the current users mailbox. The path to the mailbox is the
default system mailspool directory (usually /var/mail) with the
username as gotten from getpwuid() appended. If the environment
variable $MAIL is set, that is used instead. Then the string
".lock" is appended to get the name of the actual lockfile.

lockfile

The lockfile to be created/removed, unless the -m option is in effect.

RETURN VALUE

Zero on success, and non-zero on failure. For the -c option,
sucess means that a valid lockfile is already present. When locking
(the default, or the -l option) dotlockfile returns the same
values as the library function lockfile_create(3). Unlocking
a non-existant lockfile is not an error.

NOTES

The lockfile is created exactly as named on the command line. The
extension .lock is not automatically added.

This utility is a lot like the lockfile(1) utility included with
procmail, and the mutt_dotlock(1) utility included with
mutt. However the command-line arguments differ, and so does the
return status. It is believed that dotlockfile is the most flexible
implementation, since it automatically detects when it needs to use
priviliges to lock a mailbox, and does it safely.

The above mentioned lockfile_create(3) manpage is present
in the liblockfile-dev package.